Petroleum refining – straight-run distillation In crude oil atmospheric/vacuum distillation (without cracking), what is a typical percentage yield of straight-run naphtha obtained directly from the crude?

Introduction / Context:
In refinery practice, the crude distillation unit (CDU) and, where used, the vacuum distillation unit (VDU) separate crude oil into straight-run fractions by boiling range without chemical conversion. One of the most important light products from straight-run fractionation is naphtha, which is later treated, reformed, or isomerised for gasoline blending and petrochemical use. Knowing a typical straight-run naphtha yield helps with rough material balances and exam questions about slate distribution.

Given Data / Assumptions:

• Process: straight-run atmospheric/vacuum distillation only (no cracking or reforming).
• Desired: a typical percentage yield (by volume or weight trend) asked in exam style; choose the closest option.
• Feed: a representative medium crude; not a condensate-rich edge case.

Concept / Approach:
Crude assays for common medium crudes often show straight-run naphtha in a low-to-mid teens percent range, while lighter condensates may give higher values and heavy/sour crudes somewhat lower. Exam keys typically anchor on a simple round figure near the middle of this typical band. Among the offered choices, 12 is a standard teaching value for straight-run naphtha yield from a representative crude slate.

Step-by-Step Solution:

Verification / Alternative check:
Introductory refinery texts and crude assay tables commonly show straight-run naphtha of about 10–15 percent for medium crudes, aligning well with 12 as a round, memorable figure for examinations.

Why Other Options Are Wrong:

• 2: Unusually low; would indicate a very heavy crude or atypical cut definition.
• 6: Still lower than common medium-crude assays.
• 18: Possible for very light crudes/condensates but not representative of a typical “about” value.

Common Pitfalls:
Confusing straight-run naphtha with total gasoline after conversion (reforming/FCC), which is higher. Also mixing weight vs volume percent does not change the ordering of options here.

Final Answer:
12